Abstract: A method is disclosed for specifying the ratios of three or more coating materials so as to specify and control the index of refraction profile, stress profile, and/or the coefficient of thermal expansion of an optical coating. Also disclosed is a coating deposition chamber (10) that includes an in-situ stress monitor (12) for measuring a stress within a coating (20). The output of the monitor is compared to predicted profiles and appropriate corrections are made to chamber constants. In a presently preferred embodiment, the in-situ stress monitor includes an interferometer having a sample beam (28a) that reflects from a surface of a substrate (22) upon which the coating is being formed. A change in the optical path length is indicative of a direction and magnitude of a substrate flexure due to stress induced in the coating. Responsive to the determined stress, coating chamber operating parameters are varied, if required, to maintain the stress at a desired magnitude and type.

Abstract: A method, and apparatus for accomplishing the method, for determining a phase difference of a wavefront at a first (pupil) plane (P1), the wavefront propagating from the first plane to a second (image) plane (P2). The method includes the steps of providing an intensity of the wavefront at the first plane; measuring an intensity of the wavefront at the second plane; and determining the phase difference of the wavefront at the first plane in accordance with a transfer function that employs the provided intensity of the wavefront at the first plane and the measured intensity of the wavefront at the second plane. A single expression describing an Optical Transfer Function is developed and is shown to involve only the unknown aperture phase and known quantities. A solution to this expression, achieved by a polynomial expansion technique or by a sampling technique, is shown to yield the phase at the aperture and, together with the intensity at the aperture, to define the aperture wavefront.

Abstract: A system (10, 80) for detecting modulating laser signals having a memory (28) for storing the occurrences of a plurality of different pulse intervals in accordance with at least one preselected characteristic of the different pulse intervals and outputting a signal when a weighted sum of the number of different pulse intervals counted exceeds a preselected threshold number.

Abstract: An optical element (10) is provided with a coating so as to selectively pass spectral lines of interest. The element includes a substrate (14) having a first major surface and a second, opposite major surface. The element further includes a coating, preferably a rugate coating (12), formed upon at least one of the major surfaces. The rugate coating has a spatially varying index of refraction profile through a depth thereof. The profile is selected so as to provide the element with a prescribed dispersion characteristic that matches a dispersion characteristic of a source of the radiation signal.

Abstract: An etalon (10) is provided with a coating (12) so as to selectively pass spectral lines of interest. The etalon includes a substrate (14) having a first major surface and a second, opposite major surface. The etalon further includes a coating, preferably a rugate coating (12), formed upon at least one of the major surfaces. The rugate coating has a spatially varying index of refraction profile through a depth thereof. The profile is selected so as to provide the element with a prescribed dispersion characteristic that matches a dispersion characteristic of a source of the radiation signal.

Abstract: This invention provides embodiments of etalons (10, 14, 18, 22) that eliminate or minimize a falloff of relative radiation modulation as a function of wavelength or FOV. A first embodiment employs a dispersive coating, such as a rugate (12a, 12b, 16), to correct for the phase shift across an etalon step. A second embodiment employs a dispersive coating, such as a rugate (20a, 20b, 24), that provides a stepless etalon in which the phase shifts are generated by the coating. It is shown that in a rugate the phase shift on reflection is directly related to the phase of a sinusoidal index of refraction profile within the rugate, while the frequency of the sinusoidal index of refraction profile determines the wavelength at which the phase shift occurs. By changing the phase of the sinusoidal index of refraction variation as the period of the sinusoidal index of refraction variation is changed, a phase shift of incident radiation is produced that is a function of the wavelength of the incident radiation.

Abstract: A CW and/or pulse coherent radiation detection system (10) includes at least one radiation detector (14) having a plurality of discrete radiation detector elements (A-D) disposed upon a surface thereof. A coherence length discriminator (CLD), for example an etalon (12), is constructed so as to vary an optical path length therethrough at a plurality of locations. The CLD is disposed relative to the radiation detector such that radiation passing through the CLD is received by the discrete radiation detector elements. The apparatus further includes a drive (16) for translating the CLD relative to the radiation detector so as to modulate only coherent radiation passing through the CLD. The drive is preferably a reactionless drive having an energy consumption made small by the use of small CLD motions that correspond to the dimensions of individual detector elements. The coherent radiation detector is also shown to be usable for detecting an angle of arrival of coherent radiation.

Abstract: A time of flight velocimeter wherein a radiation source projects two parallel beams into an air mass. Each of the parallel beams converges into a waist portion. As an aerosol particle moves through the waist portion, part of the radiation of each of the beams is backscattered. This backscattered radiation is focused onto two detectors, one for each beam. Signals from the detectors, generated in response to the backscattered radiation, are processed to determine the velocity of the particle which has passed through the waist portion of the two beams.

Abstract: Apparatus for detecting the existance of a source of coherent radiation in the presence of incoherent radiation. A beam splitter splits the radiation into two paths. Means are included in one path for transmitting the incoherent radiation and modulated coherent radiation. The other path effectively transmits only the incoherent radiation. Balancing means are used to balance out the incoherent radiation transmitting only the modulated coherent radiation which is then detected.

Abstract: Apparatus for detecting and/or determining the wavelength of coherent radiation in the presence of incoherent ambient radiation. The apparatus includes at least three unequal path interferometers with the radiation path length difference in each interferometer being substantially greater than the coherence length of the incoherent radiation, but substantially less than the coherence length of the coherent radiation, the average radiation path length in said three interferometers being different one from the others. The apparatus further includes detectors for detecting the radiation transmitted through each of the interferometers for generating signals corresponding to the radiation leaving each interferometer, and electronic processing elements to detect and determine the wavelength of the coherent radiation.A preferred form of interferometer is a Fabry-Perot etalon having a plurality of regions of different thicknesses.